11927 Log, or optionally panic, on zero-length kmem allocations
Reviewed by: Dan McDonald <danmcd@joyent.com>
Reviewed by: Jason King <jason.brian.king@gmail.com>

*** 403,421 ****
  sa_add_layout_entry(objset_t *os, sa_attr_type_t *attrs, int attr_count,
      uint64_t lot_num, uint64_t hash, boolean_t zapadd, dmu_tx_t *tx)
  {
          sa_os_t *sa = os->os_sa;
          sa_lot_t *tb, *findtb;
!         int i;
          avl_index_t loc;
  
          ASSERT(MUTEX_HELD(&sa->sa_lock));
          tb = kmem_zalloc(sizeof (sa_lot_t), KM_SLEEP);
          tb->lot_attr_count = attr_count;
!         tb->lot_attrs = kmem_alloc(sizeof (sa_attr_type_t) * attr_count,
!             KM_SLEEP);
!         bcopy(attrs, tb->lot_attrs, sizeof (sa_attr_type_t) * attr_count);
          tb->lot_num = lot_num;
          tb->lot_hash = hash;
          tb->lot_instance = 0;
  
          if (zapadd) {
--- 403,424 ----
  sa_add_layout_entry(objset_t *os, sa_attr_type_t *attrs, int attr_count,
      uint64_t lot_num, uint64_t hash, boolean_t zapadd, dmu_tx_t *tx)
  {
          sa_os_t *sa = os->os_sa;
          sa_lot_t *tb, *findtb;
!         int i, size;
          avl_index_t loc;
  
          ASSERT(MUTEX_HELD(&sa->sa_lock));
          tb = kmem_zalloc(sizeof (sa_lot_t), KM_SLEEP);
          tb->lot_attr_count = attr_count;
! 
!         if ((size = sizeof (sa_attr_type_t) * attr_count) != 0) {
!                 tb->lot_attrs = kmem_alloc(size, KM_SLEEP);
!                 bcopy(attrs, tb->lot_attrs, size);
!         }
! 
          tb->lot_num = lot_num;
          tb->lot_hash = hash;
          tb->lot_instance = 0;
  
          if (zapadd) {